Active thermography is a non-destructive evaluation (NDE) technique in which energy with a certain time and/or spatial structure is applied to a test object, and a resulting temperature distribution on a surface of the object is measured with an infrared camera. From the recorded infrared sequence, information about defects, surface structure and the inner structure of the object may be obtained. The image is digitized into picture elements, or pixels, each representing a small unit area on the test object surface. The temperature/time signal is processed and evaluated per pixel and in patterns of pixels.
In active thermography, energy may be applied to a test object by electromagnetic induction, mechanical vibrations including ultrasound, flash radiation, laser, hot air, or microwave excitation. In a pulsed version of active thermography, the excitation power is switched on for a time period of typically 1 millisecond to over 1.5 seconds, depending upon the application.